Learning to Express myself

So I've recently discovered a new thing called expressing myself and setting boundaries, I've learned how to express my feelings and try to convey how I feel to people starting with my friends. I started telling them certain things hurt my feelings instead of them being empathic, they always say things like, "Ohh, get a grip, you're being too sensitive ." I don't know what to do, should I keep it all in or just express myself